The wide variations in absorber thickness characteristic of the PA chest projection routinely results in films with an underexposed mediastinum in order to obtain films with good lung field density. Thus, a large volume of lung tissue is imaged with suboptimal contrast due to the dense overlying structures of the diaphragm, mediastinum and heart. Portal equalization filters and optical masking techniques, have been used to equalize the lung and mediastinal exposures, however, they are cumbersome and time-consuming in practice requiring accurate patient positioning and filter registration. We have developed an automatic scanning equalization system that maintains optimal film exposure over the entire chest field by using a broad beam of x-rays scanned over the patient's chest to expose a conventional cassette. The patient attenuation of each point over the firm, is monitored by a detector placed behind the cassette which is in turn used to adjust the tube output to deliver the optimal film exposure and contrast. Preliminary chest phantom images obtained with this system, show excellent contrast and penetration in both the mediastinum and lung fields. We propose further refinements of this system and a comparative evaluation with conventional chest radiography by phantom studies and a clinical trial to measure its impact on the detection of lung cancer and a variety of other interstitial and alveolar pulmonary disease.